1. Field of the Invention
The present invention relates to a method and an apparatus for scanning an inner face of a cylindrical drum with dual or more light beams, and more particularly to a method and an apparatus for scanning an inner face of a cylindrical drum with plural light beams which are combined and introduced into a common optical scanning system to scan the inner face of the drum.
2. Description of the Prior Art
There is known an inner face scanning type of a light beam scanning device, wherein a light beam such as a laser beam is introduced into a cylindrical drum to scan an interior surface of the drum. To increase a recording speed in the apparatus of this type, a system with plural light beams, i.e., a multi-beam scanning system is proposed.
In the inner face scanning type of apparatus, plural light beams are introduced along a central axis of the cylindrical drum to a rotating deflector (spinner) disposed on and rotated about the central axis of the cylindrical drum. The spinner deflects incident light beams in a radial direction of the rotating drum. The spinner comprises, for example, a reflective mirror which rotates at a high speed with an angle of about 45xc2x0 with respect to the central axis of the drum. However, when plural light beams are simply introduced to the spinner with maintaining the relative positions of the light beams, relative position of the light beams after deflected by the spinner periodically varies as a rotation angle of the spinner changes. Disposition of the light beam tracks on the inner face of the drum are varied with the rotational position of the reflective surface of the spinner. Therefore, plural scanning lines recorded on the recording drum are periodically curved and cross one another. A correct scanning cannot be achieved.
To avoid the curvatures and crossover of the scanning lines, it is proposed that one light beam among the plural light beams be used as a reference beam. The reference beam is aligned with a central axis of an optical scanning system (the central axis of the recording drum) and the other light beams are rotated about the reference beam in synchronism with rotation of the spinner. With such arrangement, since an interval between the respective light beams is constant, the curved scanning lines can be straightened. Also, by changing an interval between the reference beam and the other light beams, an interval between the scanning lines can be changed with maintaining the line separation thereof.
For example, the Japanese Laid-Open Patent Publication (KOKAI) Nos. 5-27188 (corresponding to U.S. Pat. No. 5,504,619) and 5-276335 disclose a system in which a deflecting element (prism or the like) with a fixed deflection quantity is rotated in synchronism with rotation of a spinner. Also, U.S. Pat. Nos. 5,097,351 and 5,502,709 propose a system in which light beams other than a reference beam are deflected two-dimensionally.
In the former system for rotating the deflecting element with the fixed deflection quantity, there is a problem that because of the constant deflection quantity, it is impossible to change a beam interval, therefore a scanning line interval cannot be changed. Although the scanning line interval is preferably changed with a recording density, the prior system cannot vary a scanning line density in accordance with the recording density. Also, stably to rotate the deflecting element in synchronism with the spinner rotating at a high speed, a highly precise mechanical rotation transmitting mechanism is necessary. However, this mechanism is hardly available, and expensive.
In the latter system for two-dimensionally deflecting the light beams, it is necessary to use plural deflectors, such as piezo-mirrors and acousto-optic elements (acousto-optic modulators, hereinafter referred to as AOM). Further, light beams need to be deflected two-dimensionally in opposite directions in a complicated manner while keeping a constant mutual relationship in two orthogonal directions (X, Y directions). Therefore, a complicated and precise control is required, and scanning quality is hardly stabilized. This leads to an expensive device.
The present invention has been accomplished under the circumstances as aforementioned, and a first object thereof is to provide a method of simultaneously scanning an inner face of a cylindrical drum with dual light beams, in which scanning lines are straightened under a simple control without using a two-dimensional light beam deflecting element, and a scanning line interval can be changed, thereby simplifying a constitution of a system.
A second object of the present invention is to provide an apparatus for simultaneously scanning an inner face of a cylindrical drum with dual light beams, in which scanning lines are straightened under a simple control without using a two-dimensional light beam deflecting element, and a scanning line interval can be changed, thereby simplifying a constitution.
A third object of the present invention is to provide a method of simultaneously scanning an inner face of a cylindrical drum with two or more light beams, in which scanning lines are straightened under a simple control, and a scanning line interval can be easily varied with a simple constitution.
A fourth object of the present invention is to provide an apparatus for simultaneously scanning an inner face of a cylindrical drum with two or more light beams, in which scanning lines are straightened under a simple control, and a scanning line interval can be easily varied with a simple constitution.
The first object of the present invention is attained by the provision of a method for dual light beams scanning an inner face of a cylindrical drum which comprises a spinner rotating within said drum, said spinner deflecting two light beams introduced into the drum toward the inner face of the drum to scan the inner face with the two deflected light beams,
wherein said two light beams are one-dimensionally deflected in mutually orthogonal directions with each other, respectively, in synchronism with a rotation of said spinner, with keeping constant an interval between said two light beams, and then said two light beams are introduced to the spinner to be deflected to the inner surface of the drum.
In this case, on an image forming or focusing plane of the light beams, an X-Y rectangular coordinate system is assumed. The interval (distance) r between two light beams is set constant, an angular velocity of the spinner is set as xcfx89, and an offset angle of the spinner from a maximum deflecting direction is set as "psgr". The light beams are one-dimensionally deflected on an X-axis and on an Y-axis, so that a coordinate of one of the light beams on the image forming plane is (x=rxc2x7cos(xcfx89t+"psgr"), y=0) and a coordinate of the other light beam on the image forming plane is (x=0, y=rxc2x7cos(xcfx89t+"psgr")).
The second object of the present invention is attained by the provision of an apparatus for simultaneously dual light beams scanning an inner face of a cylindrical drum, comprising:
a) two deflecting elements for one-dimensionally deflecting the two light beams in mutually orthogonal directions, respectively;
b) a spinner rotating coaxially with said cylindrical drum for deflecting said two light beams incident along a central axis of the cylindrical drum to scan the inner face of the cylindrical drum;
c) angle detecting means for detecting a rotation angle of the spinner;
d) a memory for storing deflection quantities of said deflecting elements necessary for one-dimensionally deflecting the light beams in mutually orthogonal directions in synchronism with the rotation of said spinner while keeping constant an interval between the two light beams; and
e) deflecting element control means for driving said deflecting elements based on the deflection quantities stored in said memory.
In a preferable embodiment, a mechanism for compensating positions of the light beams is provided. The mechanism can be constituted as follows.
Beam position detecting means is provided for detecting image-beams or focusing are incident upon the spinner. Detected beam positions are compared with adequate positions which are obtained from adequate deflection quantities (angles) stored in the deflection quantity memory, and compensation quantities for compensating a difference between the positions are obtained and stored in a compensation quantity memory. Dual beam scanning is performed while controlling the deflection quantities by using compensation data.
When the compensating mechanism is provided, a preliminary scanning may be performed separately for each light beam prior to recording of image data. The compensation data of each light beam is obtained and stored. Therefore, influences of changes in temperature, changes in properties with an elapse of time, or the like of the optical system or the like can be eliminated. A correct, highly precise scanning can be achieved.
The compensation data may be re-written at adequate times. For example, when power is turned on, every time a predetermined time elapses, every time of output of predetermined pages of image, as required by an operator, and at other times, an instruction for re-writing can be given.
As the light beams, laser beams are suitable. In this case, as the one-dimensional light beam deflecting elements, acousto-optic modulating elements (AOM) are preferably used. The beam position detecting means can be constituted by disposing a quarter position detecting element around the image forming or focusing plane. The image focusing plane may be obtained by splitting a composite light beam with a beam splitter.
The third object of the present invention is attained by the provision of a method for scanning an inner face of a cylindrical drum with plural light beams, said drum comprising a spinner rotating on a central axis of the drum to deflect each light beam to the inner face of the drum,
wherein one light beam passes along a central axis common with said spinner and the cylindrical drum and is projected into the spinner,
and wherein other light beams are inclined in a plane including said central axis by a constant angle xcex8y which is separately predetermined for each of said other light beams and further inclined in a direction orthogonal to said plane by an angle xcfx86x which is determined in synchronism with a rotation angle xcex8 of the spinner.
In the preferable embodiment, the inclination angle xcfx86x may be determined in accordance with the formula
xcex8xe2x89xa00, then xcfx86x=xcfx86y(1xe2x88x92cos xcex8/sin xcex8), and 
xcex8=0, then xcfx86x=0.
In this manner, since the inclination angle xcfx86y in the Y-direction is a fixed value, only the inclination angle xcfx86x in the X-direction can be calculated. Therefore, especially a constitution of an arithmetic operation circuit is simplified.
Also, since a scanning line interval d can be determined by d=fxc2x7xcfx86y, in which f is a focal length of a focusing lens (converging lens), conversely, the Y-direction inclination angle xcfx86y can be determined by xcfx86y=d/f to obtain a desired interval d. Therefore, setting of the interval d between the scanning lines is very simple.
Three or more light beams can be used. In this case, one light beam (the reference beam) is placed on the central axis of the spinner, a second light beam is inclined (deflected) by xcfx86y=d/f in the Y-direction, and third and subsequent light beams are tilted by xe2x88x92xcfx86y, 2xcfx86y, xe2x88x922xcfx86y, 3xcfx86y, . . . in the Y-direction. The X-direction inclination angle xcfx86x of each light beam is obtained by the arithmetic operation using the corresponding Y-direction inclination angle xcfx86y, xe2x88x92xcfx86y, 2xcfx86y, xe2x88x922xcfx86y, 3xcfx86y, . . . .
In the above method, from the reference beam, the other light beams are deviated in time in a main scanning direction, i.e., in scanning phase. The deviation in phase can be eliminated by correcting a clock timing of an image signal. An arithmetic operation is described later.
The fourth object of the present invention is attained by a provision of an apparatus for scanning an inner face of a cylindrical drum with plural light beams, said drum having a spinner rotating on a central axis of the drum to deflect said plural light beams to the inner surface of the drum, one of the plural light beams passing along a central axis common with said spinner and the drum to be projected to the spinner, comprising:
angle detecting means for detecting a rotation angle xcfx86 of the spinner; and
a light beam deflecting element for deflecting the other light beams in a plane including said central axis by a constant angle xcfx86y which is separately predetermined for each of the other light beams, and in a direction orthogonal to said plane including a rotation axis by an angle xcfx86x which is determined in synchronism with the rotation angle xcex8 of the spinner.